hello everyone, I made a project about protection relays using the Arduino Uno microcontroller, including undervoltage, overcurrent, and low-frequency. in the project I have to simulate so that the relay can trip.
as the input voltage I use a Voltage regulator that is connected to the State Electricity Company
I use a voltage regulator in order to simulate the undervoltage, and to simulate the overvoltage I use a load.
the problem is, I don't know how to simulate the low frequency, is there a module or circuit that can change the frequency to low? in my country the frequency is 50hz, how do I make it so that it can be below 50hz?
Sorry if it's long, I hope I get an answer in this forum. thanks
This is interesting. Years ago, electronic hobbyists would often take an old/surplus AC transformer (220V to 12V as an example) and build a transistorized AC inverter to provide 120V/240V AC for the automobile, etc.
You could use a similar approach and build a small demonstration of the AC power company but design the model to have a potentiometer to slightly change the 50Hz output. It may also me possible to hack an eBay purchased 12V-120V/240V car inverter to achieve the same effect. Around here, surpluses units are common.
I think there are two requirements here. One is to monitor voltage and flag up under/over voltage; the other to monitor under (or over?) frequency.
The first is in principle easy, you have a voltmeter and monitor the value. You seem to have chosen an odd way to do that, I would just use a small transformer with say a 6V output, rectify that with 4 diodes, have a smoothing cap, a potentiometer to sample the voltage so that at "normal" it's at the centre of the Arduino supply range (2.5V for a 5V Arduino) send it to an analogue input and you're away.
Frequency is equally easy in principle - create a 50Hz square wave from the transformer output and measure its frequency. But you want to simulate that for test purposes. If you had a function generator it would be easy, just set it to 50Hz and you're off to the races. Without that, use another Arduino to generate a test signal. Use the Blink sketch and change the times to 10ms on/10ms off and you get 50Hz out at the LED pin. Change one of the numbers by + or -1 to change the frequency by +/- 5%. At the moment I've got a breadboard with 3 Nanos on my desk, two emulating other parts of the system for which I'm generating control code running on the 3rd.
I assume your frequency monitoring circuit runs at lowed voltage, maybe through a transformer, so you should be able to simulate it with an oscillator.
In most countries the line frequency is super-accurate and from what I understand they actually "count" the cycles and make tiny corrections, so if it's slightly fast for awhile they'll run it slightly slow for awhile to keep clocks accurate. Those variations should be so small that they are difficult to measure.
AC powered analog clocks use a synchronous motor so if you don't lose power it should run for years and never be 1 second off. I have a digital clock that runs off the line frequency and know that because it has a back-up battery and when I loose power it drifts-off badly. Not even close to a battery operated clock/watch... If the power is off for a couple of hours the clock is wrong by several minutes.
True in the short term here in Central Oregon. However, when the local power company switches between hydro and solar, there are glitches that cause some of my line synced clocks to all gain or loose a few seconds per week, when compared to WWVB clock. The base frequency, 60 Hz is stable, but not constant over a week or so.
That is quite interesting about accuracy especially switching between systems or connecting two or more generators in parallel, the phase/frequency would have to match or the difference in potential could cause problems. Perhaps this would be a reason to monitor frequency. Im guessing at all the above so I'm off to google how these situations are handled.
You need a motor generator set. By varying the speed of the motor you control the frequency of the generator.
For lower current applications an amplified sinewave signal generator can be set to whatever frequency you desire.
OK you have the voltage function covered. Any number of ways that can be done. So next you want the frequency function. There are a few ways but the quick and simple method is to use a function generator. I have seen inexpensive function generators on Amazon for under $30 USD. Also seeing kits like this one using the ever popular XR2206 for about $10 USD. You may even fine an old audio oscillator.
This assumes you don't need mains voltage frequency and low voltage frequency should be fine.
To change the frequency of all of your mains power requires big/expensive gear.
Question is why you want a stable frequency.
Most modern gear doesn't care about a little deviation.
Leo..
Then simulate the 50Hz with a signal generator connected to the Arduino pin you are using for frequency sensing,
If you have proven your interface circuit from mains voltage to logic level into the Uno, then just remove it and use a variable AC signal, it doesn't have to be mains, just logic level. (Simulate is the keyword here.)
I dont know where that is, but in the UK the frequency is set by the speed of rotation of generators that are locked to the grid frequency, and maintained to a VERY high standard.
Years ago wall clocks often used the mains frequency to maintain time.
Perhaps if you were running from a portable generator this might be a problem, but otherwise I dont see the need for measuring frequency.
This had a cautionary tale of what happened when much of the UK grid was brought down by some big lightning storms. The main thing to suffer was the grid frequency which dropped briefly below 49Hz. Siemens had designed new electric trains with TPWS systems (Google it) and apparently if the mains frequency dropped to 49Hz for some reason this could cause interference with the systems which are safety critical. So the software monitored the frequency and shut down the train controller, stopping the train, in a way that required someone to go to the train with a laptop to restart it. With the trains stopped all over the rail network this took some time.
So mains frequency is important and systems should be designed to take account of variations in it, preferably not by just switching off! And another site shows how the variability has increased with more renewable power as this doesn't rely on large rotating machines.
Apparently for political reasons (some countries not contributing their whack of power) the long-term average frequency in Europe is somewhat below 50Hz at the moment.
So I think the OP's project is right to include frequency monitoring!
Are you assuming that OP has poorly designed electric train?
I can't think of anything in my house that would break if the frequency was off,
well, maybe my 30-year old alarm clock-radio.
Leo..
My brother is recently retired from the power industry. In a power station they have to be very careful about matching the frequency and phase before switching a generator to supply the load. He has told me of the 'problems' this causes when not done correctly, like the rotor of a 500MW generator, weighing several hundred tonnes, jumping out of its bearings and disappearing out through the generator hall roof. Not the sort of 'problem' you want to have.
When I was a Uni, one of the Electrical Pracs was to sync a DC motor driven 3phase alternator to the labs 3phase, when in phase you hit the button that operated the 3phase contactor.
There were 3 lamps connected between the 2 3phase networks that indicated with their lack of brightness if the phases were in sync.
Those were the days.....
As @fluks is a display project, measuring frequency would be a good parameter to show.
In the US, all power generation frequencies are locked to a clock signal from GPS satellites. How secure do you think a single point failure can be? The next big solar storm could bring it all down.
